91987358521 has 4 divisors (see below), whose sum is σ = 91988822772. Its totient is φ = 91985894272.

The previous prime is 91987358459. The next prime is 91987358531. The reversal of 91987358521 is 12585378919.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12585378919 = 17 ⋅740316407.

It can be written as a sum of positive squares in 2 ways, for example, as 28400675625 + 63586682896 = 168525^2 + 252164^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-91987358521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91987358531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 633460 + ... + 765013.

It is an arithmetic number, because the mean of its divisors is an integer number (22997205693).

Almost surely, 2^91987358521 is an apocalyptic number.

It is an amenable number.

91987358521 is a deficient number, since it is larger than the sum of its proper divisors (1464251).

91987358521 is a wasteful number, since it uses less digits than its factorization.

91987358521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1464250.

The product of its digits is 5443200, while the sum is 58.

The spelling of 91987358521 in words is "ninety-one billion, nine hundred eighty-seven million, three hundred fifty-eight thousand, five hundred twenty-one".